U.S. patent application number 10/833501 was filed with the patent office on 2005-11-17 for absorbent composition having multiple surface treatments.
Invention is credited to Hu, Sheng-Hsin, Qin, Jian, Wilhelm, Hoa La.
Application Number | 20050256468 10/833501 |
Document ID | / |
Family ID | 34960362 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050256468 |
Kind Code |
A1 |
Qin, Jian ; et al. |
November 17, 2005 |
Absorbent composition having multiple surface treatments
Abstract
An absorbent composition includes absorbent material, such as
superabsorbent material, surface-treated with at least two
different compatible agents. The superabsorbent material may be
coated with multiple surface treatment agents in such a manner that
each of the surface treatment agents is exposed on a surface of the
superabsorbent material. For example, one surface treatment agent
may be in a liquid coating form and another surface treatment agent
may be in a powder form, each applied separately to the
superabsorbent material.
Inventors: |
Qin, Jian; (Appleton,
WI) ; Wilhelm, Hoa La; (Appleton, WI) ; Hu,
Sheng-Hsin; (Appleton, WI) |
Correspondence
Address: |
Melanie I. Rauch
Pauley Petersen & Erickson
Suite 365
2800 West Higgins Road
Hoffman Estates
IL
60195
US
|
Family ID: |
34960362 |
Appl. No.: |
10/833501 |
Filed: |
April 28, 2004 |
Current U.S.
Class: |
604/358 ;
524/414 |
Current CPC
Class: |
A61L 15/60 20130101 |
Class at
Publication: |
604/358 ;
524/414 |
International
Class: |
A61F 013/15; A61F
013/20; C08L 001/00; C08J 003/00; C08K 003/32 |
Claims
What is claimed is:
1. An absorbent composition, comprising: a superabsorbent material
surface-treated with at least two different agents, wherein the at
least two agents are compatible.
2. The absorbent composition of claim 1, wherein at least one of
the agents can form an ionic charge opposite an ionic charge of the
superabsorbent material.
3. The absorbent composition of claim 1, wherein the superabsorbent
material is anionic.
4. The absorbent composition of claim 1, wherein the superabsorbent
material is cationic.
5. The absorbent composition of claim 1, wherein at least one of
the agents comprises a thermoplastic material.
6. The absorbent composition of claim 1, wherein at least one of
the agents is chosen from polyglycols, polyoxides, polyalcohols,
modified celluloses, polyamines, polyquaternary ammoniums,
polyimines, polycarboxylic acids, polyamides, polyesters,
polyolefins, polystyrenes, polyurethanes, paraffin, wax, latex,
copolymers, and combinations thereof.
7. The absorbent composition of claim 1, wherein each of the at
least two different agents is exposed on a surface of the
superabsorbent material.
8. The absorbent composition of claim 1, wherein the superabsorbent
material is surface crosslinked before either of the at least two
agents is applied to the superabsorbent material.
9. The absorbent composition of claim 1, wherein a first agent
forms a continuous layer on the superabsorbent material, a second
agent forms a discontinuous layer on top of the first agent, and an
additional substance forms a continuous layer over both the first
agent and the second agent.
10. The absorbent composition of claim 1, wherein a first agent
forms a continuous layer on the superabsorbent material, a second
agent forms a discontinuous layer on top of the first agent, and an
additional substance forms a discontinuous layer on top of the
first agent such that the second agent and the additional substance
together form a continuous layer on top of the first agent.
11. The absorbent composition of claim 1, wherein the absorbent
composition possesses wet stickiness, as determined by the Wet
Stickiness Test, and thermal stickiness, as determined by the
Thermal Stickiness Test.
12. The absorbent composition of claim 1, wherein the
surface-treated superabsorbent material has a free swell gel bed
permeability between about 50.times.10.sup.-8 and about
500.times.10.sup.-8 cm.sup.2.
13. The absorbent composition of claim 1, wherein the
surface-treated superabsorbent material has a 0.3 psi swell gel bed
permeability between about 10.times.10.sup.-8 and about
50.times.10.sup.-8 cm.sup.2.
14. The absorbent composition of claim 1, wherein the
surface-treated superabsorbent material has a centrifuge retention
capacity between about 20 and about 50 grams per gram.
15. An absorbent article comprising the absorbent composition of
claim 1.
16. An absorbent core comprising at least 65% by weight of the
absorbent composition of claim 1.
17. An absorbent article comprising an outer cover, a body side
liner, and the absorbent core of claim 16 positioned between the
outer cover and the body side liner, wherein the absorbent core is
unwrapped.
18. An absorbent composition, comprising: a highly
surface-crosslinked anionic superabsorbent material; a first
treatment agent of polyvinyl amine applied to a surface of the
superabsorbent material at between about 0.01% and about 10% by
weight of the superabsorbent material; and a second treatment agent
of polyethylene oxide powder applied to the surface of the
superabsorbent material at between about 0.01% and about 10% by
weight of the superabsorbent material, wherein the first treatment
agent and the second treatment agent are both exposed on a surface
of the superabsorbent material.
19. A method of coating superabsorbent particles, comprising:
applying a first surface treatment agent to a superabsorbent
material; and applying a second surface treatment agent to the
superabsorbent material; wherein each of the first and second
surface treatment agents is exposed on a surface of the
superabsorbent material.
20. The method of claim 19, wherein the first surface treatment
agent comprises a water-soluble coating agent.
21. The method of claim 19, wherein the first surface treatment
agent comprises at least one of the group consisting of polyvinyl
amine, polyquaternary ammonium, polyimine, and polyacrylic
acid.
22. The method of claim 19, wherein the second surface treatment
agent comprises at least one of the group consisting of a
water-soluble bonding agent, a water-insoluble bonding agent, and a
water-dispersible bonding agent.
23. The method of claim 19, wherein the second surface treatment
agent comprises at least one of the group consisting of
polyethylene oxide, polyethylene glycol, polypropylene oxide,
polypropylene glycol, modified cellulose, modified starch,
polyethylene, polypropylene, polyester, polyamide, polystyrene,
polyurethane, latex, wax, paraffin, and polyvinyl alcohol.
24. The method of claim 19, comprising applying the first surface
treatment agent to the superabsorbent material in a liquid coating
form, and applying the second surface treatment agent to the
superabsorbent material in a powder form.
25. The method of claim 24, further comprising wetting the
superabsorbent material with a solvent subsequent to applying the
first surface treatment agent and prior to applying the second
surface treatment agent to the superabsorbent material.
26. The method of claim 19, comprising preparing an emulsion
comprising the first and second surface treatment agents and
simultaneously applying the first and second surface treatment
agents to the superabsorbent material by applying the emulsion to
the superabsorbent material.
27. The method of claim 19, comprising using a fluidized bed
process to apply the first and second surface treatment agents to
the superabsorbent material.
28. The method of claim 19, comprising: introducing the
superabsorbent material into a coating chamber of a coating
apparatus; introducing a gaseous flow into the coating chamber;
spraying the first surface treatment agent into the coating
chamber, wherein the first surface treatment agent is in liquid
form; and introducing the second surface treatment agent into the
coating chamber, wherein the second surface treatment agent is in
powder form.
Description
BACKGROUND OF THE INVENTION
[0001] Personal care manufacturers are making thinner and more
discreet products for consumers while, at a minimum, maintaining
the product overall performance. This requires manufacturers to use
higher amounts of superabsorbent materials (SAM), also known as
absorbent gelling materials, and less pulp fibers than they have
with conventional products.
[0002] Products with a high content of superabsorbent material tend
to experience problems that are not encountered in products with
low superabsorbent content. One such issue is poor superabsorbent
containment. For example, in an absorbent core having a high
quantity of SAM and a low amount of fibers, there may be
insufficient fibers to hold or capture the SAM in the structure and
to prevent the SAM from falling outside the core. This poor SAM
containment issue could happen with structures having high SAM
content under both dry and wet conditions. As an additional issue,
poor structure integrity may lead to gel blocking. Gel blocking can
be seen as a phenomenon in which SAMs pack themselves in the
interstitial spaces in the core structure as the SAMs undergo
rearrangements or deformation due to external forces from a wearer.
This rearrangement of the SAM can result in lack of void volume
available in the absorbent core, which can lead to poor intake of
bodily fluid.
[0003] Manufacturers have been attempting to resolve these issues
by incorporating thermoplastic binder fibers or hot melt adhesive
in absorbent core structures to provide some attachment between
SAMs or SAMs and fibers. These approaches may restrict the swelling
of the SAMs and, thus, reduce the overall absorbency performance of
the absorbent core. Also, these approaches often require use of
large amounts of binder fibers and/or adhesives to sufficiently
hold the structure together, which may undesirably result in
increased stiffness of the absorbent pad.
[0004] There is thus a need, or desire, for a superabsorbent
material that is capable of providing both wet and dry adhesion.
There is a further need, or desire, for an absorbent pad that is
thin and has good wet and dry structure integrity without
compromising its absorbency performance. There is yet a further
need, or desire, for a method of coating superabsorbent materials
to achieve a superabsorbent material that is capable of delivering
multiple functions.
SUMMARY OF THE INVENTION
[0005] The invention includes an absorbent material that is
surface-treated or coated with at least two different agents such
that the agents are compatible. These agents are herein referred to
interchangeably as "agents" and "surface treatment agents." An
example is a superabsorbent material coated with two different
agents both of which are exposed on a surface of the superabsorbent
material. As another example, at least one of the surface treatment
agents is of opposing charge to that of the superabsorbent
material, and at least one of the other surface treatment agents is
a bonding agent. In a further example, at least one of the surface
treatment agents can form an ionic charge opposite an ionic charge
of the superabsorbent material. The superabsorbent material may be
either cationic or anionic.
[0006] The surface treatment agents may include, but are not
limited to, polyglycols, polyoxides, polyalcohols, modified
celluloses, polyamines, polyquatemary ammoniums, polyimines,
polycarboxylic acids, polyamides, polyesters, polyolefins,
polystyrenes, polyurethanes, paraffin, wax, latex, and combinations
thereof. For example, one of the surface treatment agents may
include a hydrophilic thermoplastic material, such as polyethylene
oxide.
[0007] One suitable surface treatment agent may include a
water-soluble coating agent, such as polyvinyl amine (PVAm).
Another suitable surface treatment agent applied to the same
superabsorbent material may include a bonding agent. The bonding
agent may be water-soluble, water-insoluble, or water-dispersible,
and either thermoplastic or non-thermoplastic. Examples of suitable
bonding agents include latex, polyethylene oxide, polypropylene
oxide, polyethylene glycol, hydroxypropyl cellulose, modified
starch, polyethylene, polyester, polyamide, polyvinyl alcohol,
and/or copolymers or mixtures thereof.
[0008] For example, one surface treatment agent may be applied to
the superabsorbent material in a liquid coating form, and another
surface treatment agent may be applied to the superabsorbent
material in a solid, partially dry, or dry particulate or powder
form. For instance, the liquid coating agent may be applied to the
superabsorbent material in a continuous film, and after the liquid
coating has dried or partially dried, the superabsorbent material
can be wetted as needed with an organic solvent, an aqueous
solution, or water prior to applying the dry or partially dry
powder. Alternatively, the superabsorbent material and the dry or
partially dry powder may be combined in a coating chamber of a
coating apparatus, into which a gaseous flow may be introduced
while spraying a liquid coating agent into the coating chamber,
thereby atomizing the liquid coating agent within the coating
chamber.
[0009] In another example, the surface treatment agents may be
combined in an emulsion and the emulsion may be applied to the
superabsorbent material, thereby coating the superabsorbent
material with both surface treatment agents in a single step. The
emulsion solution may include a water-soluble coating agent, such
as PVAm, and a water-dispersible adhesive, such as latex particles
suspended in the PVAM solution. The emulsion of two separate phases
can be introduced into a fluidized bed process to coat the
superabsorbent material.
[0010] In yet another example, superabsorbent materials may be
introduced into a fluidized coating chamber. A stream of PVAm
solution and another separate stream of organic solvent containing
water-soluble adhesive particles (or a separate stream of an
aqueous solution containing water-insoluble or water-dispersible
adhesive particles) may simultaneously or subsequently be atomized
onto the surface of the superabsorbent materials.
[0011] The absorbent composition possesses wet stickiness, as
determined by the Wet Stickiness Test, described below. The
absorbent composition also possesses dry stickiness, as determined
by the Thermal Stickiness Test, described below. The free swell gel
bed permeability of the absorbent composition may be between about
50.times.10.sup.-8 and about 500.times.10.sup.-8 cm.sup.2. The 0.3
psi swell gel bed permeability of the absorbent composition may be
between about 10.times.10.sup.-8 and about 50.times.10.sup.-8
cm.sup.2. The centrifuge retention capacity of the absorbent
composition may be between about 20 and about 50 grams per
gram.
[0012] With the foregoing in mind, it is a feature and advantage to
provide absorbent compositions that possess multiple surface
treatments and can thus deliver multiple attributes, as well as
methods of coating superabsorbent material to achieve such
absorbent compositions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other objects and features will be better
understood from the following detailed description taken in
conjunction with the drawings, wherein:
[0014] FIGS. 1 and 2 are diagrams of superabsorbent materials
having multiple surface treatments and having the functionality of
multiple surface treatments.
[0015] FIGS. 3 and 4 are diagrams of superabsorbent materials
having single surface treatments.
[0016] FIGS. 5-8 are diagrams of superabsorbent materials treated
with multiple surface treatments but having the functionality of a
single surface treatment.
[0017] FIG. 9 is a diagram of superabsorbent material treated with
multiple surface treatments and having the functionality of
multiple surface treatments.
[0018] FIG. 10 is a perspective view of an absorbent article into
which an absorbent composition may be incorporated.
[0019] FIG. 11 depicts apparatus used to measure free swell or 0.3
psi swell permeability of either free-flowing particles or
absorbent composites.
[0020] FIG. 12 depicts a bottom view of the apparatus of FIG.
11.
DEFINITIONS
[0021] Within the context of this specification, each term or
phrase below will include the following meaning or meanings.
[0022] "Agents" or "surface treatment agents" comprise substances
that do not form crosslinking, such as reacting with pendant
functional groups of superabsorbent macromolecules to form "bridge"
points between the polymer chains, upon, during, or at completion
of the surface treatment or coating process.
[0023] "Compatibility" or "compatible" describes two or more
surface treatment agents that, after coming into contact with each
other and/or with a substrate which they coat, each maintains its
individual original properties or functions and is able to deliver
those functions/properties in use from the surface of the substrate
or material which it coats.
[0024] "Hydrophilic" describes surfaces and fibers, or the surfaces
of fibers, which have a high affinity for aqueous liquids and are
wetted by the aqueous liquids when in contact with the surfaces.
The degree of wetting of the materials can, in turn, be described
in terms of the contact angles and the surface tensions of the
liquids and materials involved. Equipment and techniques suitable
for measuring the wettability of particular fiber materials or
blends of fiber materials can be provided by a Cahn SFA-222 Surface
Force Analyzer System available from Thermo Electron Corporation in
Madison, Wis., U.S.A., or a substantially equivalent system. When
measured with this system, fibers or surfaces having contact angles
of less than 90.degree. are designated "wettable" or hydrophilic,
while fibers or surfaces having contact angles greater than
90.degree. are designated "nonwettable" or hydrophobic.
[0025] "Ionic-interaction-enhancing agent" refers to an agent
having an ionic charge, or capable of forming an ionic charge, that
is opposite an ionic charge of the material being treated or of
other particles with which the agent comes in contact.
[0026] "Polymers" include, but are not limited to, homopolymers,
copolymers, such as for example, block, graft, random and
alternating copolymers, terpolymers, etc. and blends and
modifications thereof. Furthermore, unless otherwise specifically
limited, the term "polymer" shall include all possible
configurational isomers of the material. These configurations
include, but are not limited to isotactic, syndiotactic and atactic
symmetries.
[0027] "Powder" includes materials in particulate form of any shape
or size, including chopped fibers such as binder fibers.
[0028] "Superabsorbent" refers to a water-swellable,
water-insoluble organic or inorganic material capable, under the
most favorable conditions, of absorbing at least about 10 times its
weight, or at least about 15 times its weight, or at least about 25
times its weight in an aqueous solution containing 0.9 weight
percent sodium chloride. The superabsorbent materials can be
natural, synthetic, and modified natural polymers and materials. In
addition, the superabsorbent materials can be inorganic materials,
such as silica gels, or organic compounds such as cross-linked
polymers. The superabsorbent material may be biodegradable or
non-biodegradable. The superabsorbent materials can include
particles, fibers, tows, flakes, films, foams, and the like. A
material is "absorbent" if it absorbs at least five times its
weight of the aqueous solution under these conditions.
[0029] "Surface" refers to an outermost or exterior boundary of a
particle. The surface of a particle is that which is exposed to the
atmosphere.
[0030] "Surface treatment" or "surface treating" refers to the
application of an agent onto the surface of a particle, thereby
covering at least a portion of the surface of the particle.
[0031] "Thermoplastic" is meant to describe a material that softens
and/or flows when exposed to heat and which substantially returns
to its original hardened condition when cooled to room
temperature.
[0032] "Absorbent article" includes, but is not limited to,
personal care absorbent articles, health/medical absorbent
articles, and household/industrial absorbent articles.
[0033] "Personal care absorbent article" includes, but is not
limited to, absorbent articles such as diapers, diaper pants, baby
wipes, training pants, absorbent underpants, child care pants,
swimwear, and other disposable garments; feminine care products
including sanitary napkins, wipes, menstrual pads, menstrual pants,
panty liners, panty shields, interlabials, tampons, and tampon
applicators; adult-care products including wipes, pads, containers,
incontinence products, and urinary shields; clothing components;
bibs; athletic and recreation products; and the like.
[0034] "Health/medical absorbent article" includes a variety of
professional and consumer health-care products including, but not
limited to, products for applying hot or cold therapy, medical
gowns (i.e., protective and/or surgical gowns), surgical drapes,
caps, gloves, face masks, bandages, wound dressings, wipes, covers,
containers, filters, disposable garments and bed pads, medical
absorbent garments, underpads, and the like.
[0035] "Household/industrial absorbent articles" include
construction and packaging supplies, products for cleaning and
disinfecting, wipes, covers, filters, towels, disposable cutting
sheets, bath tissue, facial tissue, nonwoven roll goods,
home-comfort products including pillows, pads, cushions, masks and
body care products such as products used to cleanse or treat the
skin, laboratory coats, cover-alls, trash bags, stain removers,
topical compositions, laundry soil/ink absorbers, detergent
agglomerators, lipophilic fluid separators, and the like.
[0036] These terms may be defined with additional language in the
remaining portions of the specification.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] In accordance with the invention, absorbent compositions
having multiple surface treatments are provided for use in a
variety of absorbent articles. Absorbent articles containing these
absorbent compositions are also provided. A method of making these
absorbent compositions is also provided.
[0038] Absorbent materials treated with multiple surface treatment
agents typically result in just one of the agents being exposed on
the surface of the absorbent material. For example, if the surface
treatment agents are not compatible, the effect of each surface
treatment agent may be reduced or even eliminated. The
compatibility of multiple surface treatment agents may depend on
either or both the chemistry and the structural arrangement of the
surface treatment agents. For example, the surface treatment agents
are non-reactive with each other in order to be chemically
compatible. As another example, the surface treatment agents are
located in a suitable structural arrangement in order for each of
the surface treatment agents to deliver their respective
functions.
[0039] Some absorbent compositions consistent with the invention
are designed to include multiple surface treatment agents on a
superabsorbent material with each of the surface treatment agents
exposed on the surface of the superabsorbent material. The surface
treatment agents are chemically compatible with one another and/or
are structurally arranged in such a way that each surface treatment
agent is able to deliver its respective function.
[0040] As shown in FIGS. 1 and 2, the superabsorbent material 20
can include a first surface treatment agent 22 and a second surface
treatment agent 24, and both treatment agents are exposed on the
surface of the superabsorbent material 20. Additional surface
treatment agents may be included, but for simplicity, the figures
herein illustrate just two surface treatment agents. The figures
are used merely for illustration purposes, and there is no
intention to limit the structure or morphology of the invention to
the treated superabsorbent materials illustrated in the
accompanying figures. The two agents can be either
continuous/discontinuous, or discontinuous/discontinuous, or any
discontinuous shapes as long as both of the agents are exposed on
the surface.
[0041] Typically when a single surface treatment agent, such as the
first surface treatment agent 22 or the second surface treatment
agent 24, is applied alone, the single surface treatment agent
coats the superabsorbent material 20, as shown in FIGS. 3 and
4.
[0042] When two surface treatment agents are used and both of the
surface treatment agents require application on the outermost
surface of the superabsorbent material, the manner of applying the
two surface treatment agents in order to have the agents be
compatible needs some consideration. If a first surface treatment
agent 22 is simply continuously applied to a superabsorbent
material 20 followed by the application of a second surface
treatment agent 24 also in a continuous coating, the resulting
superabsorbent material 20 displays the characteristics of just the
latter-applied surface treatment agent 24, as shown in FIG. 5.
Likewise, when the second surface treatment agent 24 is applied
first, the resulting superabsorbent material 20 may display the
characteristics of just the latter-applied first surface treatment
agent 22, as shown in FIG. 6.
[0043] When the first and second surface treatment agents 22, 24
are mixed prior to applying the surface treatment agents to the
superabsorbent material 20, the surface treatment agents 22, 24 may
compete with one another and the properties of one of the surface
treatment agents, such as the one of greater volume, may dominate
the surface of the superabsorbent material 20, as shown in FIGS. 7
and 8.
[0044] The following methods and configurations are examples of
achieving multiple surface treatment agents on a superabsorbent
material with each of the surface treatment agents exposed on the
surface of the superabsorbent material, as illustrated in FIGS. 1
and 2. The terms "first surface treatment agent" and "second
surface treatment agent" are used interchangeably, with separate
terms being used merely to indicate that at least two different
surface treatment agents are present.
[0045] For example, a first surface treatment agent 22 can be
applied to the superabsorbent material 20 as a liquid coating,
using a conventional continuous or discontinuous coating process. A
second surface treatment agent 24 can then be applied in a dry
powder form in a discontinuous manner over the first surface
treatment agent 22 using a dry powder surface coating process,
resulting in a structure as shown in FIG. 9. The second surface
treatment agent 24 such as the powder can be applied to the
superabsorbent material 20 coated with the first surface treatment
agent 22 by, for example, wetting the first surface treatment
coating 22 on the superabsorbent surface with water or aqueous
solution or the like and attaching the powder to the first surface
treatment agent 22 in a discontinuous pattern, or by
suspending/mixing the powder in water or aqueous solution or the
like and applying, such as by spraying or mixing, the powder
solution mixture over the first surface treatment agent 22 coating,
or by at least partially wetting the powder with water or aqueous
solution or the like and attaching the at least partially wet
powder to the first surface treatment agent 22 coating on the
superabsorbent surface. In order to keep the second surface
treatment agent 24 from dissolving during the coating process, if
it is water-soluble, a small amount of organic solvent (about 30%
or less by weight of the second surface treatment agent) or a
mixture of water and an organic solvent can be used. Examples of
suitable organic solvents include acetone, methanol, ethanol,
isopropanol, ethylene glycol, and propylene glycol. Alternatively,
the second surface treatment agent 24 may be a water-insoluble,
thermoplastic powder, in which case there is no need for concern
regarding any dissolving issues during the coating process.
Examples of suitable water-insoluble thermoplastic powders include
polyethylene, polypropylene, polystyrene, polyester, polyamide,
polyvinyl alcohol, polyurethane, wax, paraffin, and combinations
thereof.
[0046] In some examples, one of the surface treatment agents may be
a hydrophilic or water-soluble, thermoplastic polymer, such as
polyethylene oxide, polypropylene oxide, hydroxypropyl cellulose,
polyethylene imine, polyvinyl alcohol, or polyethylene glycol.
Surface treatment agents of this type tend to cause superabsorbent
materials to stick together upon heating, resulting in thermal
stickiness, which is described in greater detail below. Such
stickiness can be used to improve superabsorbent particle
containment within an absorbent product, and can also reduce
gel-on-skin issues.
[0047] In another example, two (or more) surface treatment agents
may be applied to the superabsorbent material in a single-step
process. Dry superabsorbent material and a first surface treatment
agent in a dry powder form, such as polyethylene oxide powder, can
be introduced into a coating chamber of a coating apparatus. A
spray nozzle may be mounted at the center of the chamber. An inlet
airflow may be adjusted to fluidize the superabsorbent material and
the dry-powder first surface treatment agent. A second surface
treatment agent in solution form, such as a polyvinyl amine
solution, may be introduced through the nozzle and atomized into
the chamber containing the fluidized superabsorbent material and
dry-powder first surface treatment agent. The second surface
treatment agent solution is atomized by the air in the chamber. The
second surface treatment agent solution catches the dry-powder
first surface treatment agent and adheres to the superabsorbent
material.
[0048] A wide variety of fluidized bed coating systems can be
adapted to coat superabsorbent materials with surface treatment
agents. For example, one can use a Wurster Fluid Bed Coater such as
the Ascoat Unit Model 101 of Lasko Co. (Leominster, Mass.), the
Magnacoater.RTM. by Fluid Air, Inc. (Aurora, Ill.), or the modified
Wurster coater described in U.S. Pat. No. 5,625,015, issued Apr.
29, 1997, to Brinen et al., which is hereby incorporated by
reference in its entirety in a manner consistent with the present
document. The coater is typically configured as a cylindrical or
tapered vessel (larger diameter at the top than at the bottom) with
air injection at the bottom through air jets or a distributor plate
having multiple injection holes. Superabsorbent material and powder
surface treatment agents are fluidized in the gaseous flow. One or
more spray nozzles inject another coating material initially
provided as a liquid, slurry, or foam at a point where good contact
with the moving fibers and/or particles can be achieved. The
superabsorbent material and powder surface treatment agent move
upwards and descend behind a wall or barrier, from whence the
particles can be guided to again enter the fluidized bed and be
coated again, or can be removed and further processed. Elevated air
temperature or the application of other forms of energy
(microwaves, infrared radiation, electron beams, ultraviolet
radiation, steam, and the like) causes drying or curing of the
coating material on the fibers and/or particles. The superabsorbent
material and powder surface treatment agent can be recycled through
the fluidized bed a plurality of times to provide the desired
amount of the other surface treatment agent on the superabsorbent
material.
[0049] The surface treatment agents can be applied by many methods
such as pan coating, spray coating, fluidized bed coating, and the
like. The original Wurster fluid bed coaters are described in U.S.
Pat. No. 2,799,241, issued Jul. 16, 1957, to D. E. Wurster; U.S.
Pat. No. 3,089,824, issued May 14, 1963, to D. E. Wurster; U.S.
Pat. No. 3,117,024, issued Jan. 7, 1964, to J. A. Lindlof et al.;
U.S. Pat. No. 3,196,827, issued Jul. 27, 1965, to D. E. Wurster and
J. A. Lindlof; U.S. Pat. No. 3,207,824, issued Sep. 21, 1965, to D.
E. Wurster et al.; U.S. Pat. No. 3,241,520 issued Mar. 21, 1966, to
D. E. Wurster and J. A. Lindlof; and U.S. Pat. No. 3,253,944,
issued May 31, 1966, to D. E. Wurster; all of which are herein
incorporated by reference in their entirety in a manner consistent
with the present document. More recent examples of the use of
Wurster coaters are given in U.S. Pat. No. 4,623,588, issued Nov.
18, 1986, to Nuwayser et al., which is hereby incorporated by
reference in its entirety in a manner consistent with the present
document. A related device is the coater of H. Littman disclosed in
U.S. Pat. No. 5,254,168, "Coating Apparatus Having Opposed
Atomizing Nozzles in a Fluid Bed Column," issued Oct. 19, 1993,
which is hereby incorporated by reference in its entirety in a
manner consistent with the present document.
[0050] The typical size of superabsorbent particles is around 150
microns to 800 microns. The surface treatment dry powder used in
certain examples herein may be present as a finely divided solid,
with particles smaller than 150 microns in maximum dimension.
[0051] In another example, the first and second surface treatment
agents may be combined to form an emulsion by mixing or suspending
one of the surface treatment agents, such as latex particles, in an
oil phase and the other surface treatment agent, such as polyvinyl
amine, in a water phase. The emulsion includes two separate phases,
which can then be introduced into a coating apparatus, such as a
fluidized bed coating system, to coat the superabsorbent
material.
[0052] In order for all surface treatment agents to be exposed on
the surface of the superabsorbent material as described in the
examples above, only one of the surface treatment agents when they
are both stable upon contact with bodily wastes, at most, may form
a continuous film or layer on the surface of the treated
superabsorbent. The second surface treatment agent has to be formed
in a discontinuous fashion on top of the continuous or
discontinuous layer of the first surface treatment agent.
[0053] For example, a first surface treatment agent may be an
ionic-interaction enhancing agent and a second surface treatment
agent may be a thermally sticky agent. An
ionic-interaction-enhancing agent can form an ionic charge opposite
an ionic charge of the superabsorbent material, and a thermally
sticky agent is a thermoplastic material capable of becoming sticky
when it is exposed to a temperature higher than its melting or
softening temperature. The first surface treatment agent can be
applied to the surface of the superabsorbent material continuously
first, since ionic-interaction enhancing agents tend to promote
inter-particle interaction or attraction when the treated particles
are wet, and the second surface treatment agent can then be applied
on top of the first surface treatment agent discontinuously.
Furthermore, both the ionic-interaction-enhancing agent and the
thermally sticky agent should be on the outermost surface of the
superabsorbent material in order to deliver inter-particle
attraction when wet and to form inter-particle bonds upon heating
to provide dry structure integrity. If these two surface treatment
agents were both applied continuously, the second surface treatment
agent would obscure the first surface treatment agent's functional
attributes, and only the second surface treatment agent would be
functional.
[0054] Examples of suitable thermally sticky agents include
polyethylene oxide, polypropylene oxide, hydroxypropyl cellulose,
polyethylene imine, polyvinyl alcohol, polyethylene glycol,
polyethylene, polyacrylate, polystyrene, polyamide, and
combinations thereof. Examples of surface treatment agents having
an opposite charge to that of the superabsorbent materials, also
known as ionic-interacting-enhancing agents, include linear
cationic polymers and linear anionic polymers. The
ionic-interacting-enhancing agent does not cause a significant
reduction in absorbent capacity and, in addition, may enhance
inter-particle interaction after the treated superabsorbent
material is wet. The inter-particle interaction may be so strong
that it causes particles to stick together due to inter-particle
ionic attraction, since the surface of the treated superabsorbent
material contains both cationic and anionic regions in a swollen
state. The ionic interaction may improve the wet integrity of the
superabsorbent material and may significantly enhance the fluid
permeability and intake function of the superabsorbent material due
to the generation of air pockets caused by a combination of
superabsorbent material swelling and formation of inter-particle
ionic bonds.
[0055] The surface treatment agents may include bonding agents or
coating agents, either water-soluble, water-insoluble, or
water-dispersible. In general, examples of suitable surface
treatment agents include polyglycols, such as polyethylene glycol,
polypropylene glycol, polyethylene-propylene glycol copolymer;
polyoxides, such as polyethylene oxide, polypropylene oxide,
polyethylene-propylene oxide copolymer; polyalcohols, such as
polyvinyl alcohol, polyvinyl alcohol copolymer; modified
celluloses, such as hydroxypropyl cellulose, hydroxyethyl
cellulose, methyl ethyl cellulose; polyquatemary ammoniums, such as
polydiallyl dimethyl ammonium hydroxide; polyamines, such as
polyvinyl arnine; polyimines, such as polyethylene imine;
polycarboxylic acids, such as polyacrylic acid, carboxymethyl
cellulose; polyamides, such as polycaproamide; polyesters, such as
polymethyl methacrylate, polytetramethylene terephthalate;
polyolefins, such as polyethylene, polypropylene; polystyrenes;
polyurethanes; paraffin; wax; latex; and mixtures or copolymers of
all the above, such as polyacrylic acid-methyl methacrylate
copolymer, polyacrylic acid-polyethylene copolymer, and the like.
Two or more of these surface treatment agents, when used in
combination as described herein, should be chemically compatible
with one another and/or structurally arranged in such a way that
each surface treatment agent is able to deliver its respective
function.
[0056] One example of a suitable first surface treatment agent is
polyvinyl amine solution, available from BASF Corporation in Mount
Olive, N.J., under the trade name CATIOFAST.RTM. PR8106 (23 wt %
solids). The polyvinyl amine solution can be dissolved in distilled
water, to which the superabsorbent material may be added and
stirred. After swelling, the superabsorbent material can be dried,
such as at about 60 degrees Celsius for about 15 hours or longer.
The dried superabsorbent material can be ground and screened
through a sieve.
[0057] One example of a suitable second surface treatment agent is
polyethylene oxide powder, available from Union Carbide in Danbury,
Conn., under the trade name POLYOX.RTM. 205. The powder can be
attached or coated to the surface of the superabsorbent material
over the first surface treatment agent via water or an aqueous
solution comprising an organic solvent such as an isopropyl
alcohol/water mixture.
[0058] The surface-treated superabsorbent material suitably
contains between about 0.01% and about 10%, or between about 0.1%
and about 5% by weight of each of the surface treatment agents. In
certain examples, equal amounts of each of the surface treatment
agents may be applied to the superabsorbent material, however, an
even ratio is not required.
[0059] It is also contemplated that a superabsorbent material may
be coated or surface treated with at least two different agents
wherein the outermost agent coating is a continuous layer. Under
certain conditions, such as upon contact with bodily waste or
fluid, the outermost layer or coating at least partially dissolves
or disperses to unveil at least a portion of the underlying agent
coating.
[0060] It is also contemplated that a superabsorbent material may
be coated or surface treated with at least two different agents
wherein the first agent forms a continuous layer and the second
agent forms a discontinuous coating on top of the continuous layer
of the first agent. An additional substance, distinct from at least
the second agent, may be applied to the treated superabsorbent
material to form either a continuous layer over both the first and
second agents, or a discontinuous layer that partially covers the
first and/or second agents. For example, the additional substance
in combination with a discontinuous layer of the second surface
treatment agent may form a continuous layer over the first surface
treatment agent. The additional substance may be an inert material,
which may partially or fully dissolve or disperse upon contact with
bodily wastes to unveil at least a portion of the underlying
coating agent or agents.
[0061] The superabsorbent materials can include particulates,
flakes, fibers, films, foams, non-ionic superabsorbents, and/or
ionic superabsorbents, sodium polyacrylate superabsorbents, for
example. The superabsorbent materials can be selected from natural,
synthetic, and modified natural polymers and materials. The
superabsorbent materials can be inorganic materials, such as silica
gels, or organic compounds, such as crosslinked polymers.
Conventional superabsorbent materials are crosslinked
polyelectrolytes. Polyelectrolytes include either anionic or
cationic polymers. Anionic polymers contain functional groups such
as carboxyl, sulfonate, sulphate, sulfite, phosphate, or a mixture
thereof. Examples of anionic polymers include, but are not limited
to, salts or partial salts of polyacrylic acid, polyacrylamido
methylpropane sulfonic acid, polyvinyl acetic acid, polyvinyl
phosphonic acid, polyvinyl sulfonic acid, isobutylene-maleic
anhydride copolymer, carboxymethyl cellulose, alginic acid,
carrageenan, polyaspartic acid, polyglutamic acid, and copolymers
or mixtures thereof. Cationic polymers contain functional groups
such as primary, secondary, and tertiary amine, imine, amide,
quaternary ammonium, or mixtures thereof. Examples of cationic
polymers include, but are not limited to, salts or partial salts of
polyvinyl amine, polydiallyl dimethyl ammonium hydroxide,
polyacrylamidopropyl trimethyl ammonium hydroxide, polyamino
propanol vinyl ether, polyallylamine, chitosan, polylysine,
polyglutamine, and copolymers or mixtures thereof. Examples of
commercially available superabsorbent materials include SXM 9394,
SXM 9543, and FAVOR 880, each available from Degussa Superabsorber
in Greensboro, N.C., U.S.A., and Dow DRYTECH 2035HP, available from
Dow Chemical Co. in Midland, Mich., U.S.A. These and other
superabsorbent materials, including biodegradable superabsorbents,
are suitable for use in the absorbent compositions. The
superabsorbent material may include pre-screened 300-600 micron
particles.
[0062] The term "polymer," as used herein, refers to either a
single polymer or to a mixture of polymers. The term "anionic
polymer," as used herein, refers to a polymer or mixture of
polymers including a functional group or groups having a potential
for becoming negatively charged ions upon ionization in an aqueous
solution. The term "cationic polymer," as used herein, refers to a
polymer or mixture of polymers including a functional group or
groups having a potential for becoming positively charged ions upon
ionization in an aqueous solution.
[0063] The absorbent compositions including the superabsorbent
material having multiple surface treatments may have considerable
absorbent capacity and gel strength. Gel strength of the
superabsorbent material is assessed herein using 0.3 psi pressure
swell gel bed permeability (GBP), described in detail in the Test
Methods section below. The surface-treated superabsorbent material
included in the absorbent compositions described herein suitably
has a 0.3 psi pressure swell GBP of about 10 to about 50
(.times.10.sup.-8 cm.sup.2), or about 20 to about 50
(.times.10.sup.-8 cm.sup.2), or about 30 to about 50
(.times.10.sup.-8 cm.sup.2). The surface-treated superabsorbent
material included in the absorbent compositions suitably has a free
swell gel bed permeability (GBP) of about 50 to about 500
(.times.10.sup.-8 cm.sup.2), or about 100 to about 500
(.times.10.sup.-8 cm.sup.2), or about 200 to about 500
(.times.10.sup.-8 cm.sup.2), as determined by the free swell GBP
Test Method described in detail below, and a centrifuge retention
capacity (CRC) between about 20 and about 50 grams/gram, or between
about 25 and about 40 grams/gram, as determined by the CRC Test
Method described in detail below. Additionally, in certain
examples, the surface-treated superabsorbent material or absorbent
composition may possess wet stickiness, as determined by the Wet
Stickiness Test Method described in detail below. The absorbent
composition may also possess thermal stickiness, as determined by
the Thermal Stickiness Test Method described in detail below.
[0064] In addition to the superabsorbent material having multiple
surface treatments, the invention may also include absorbent cores
or absorbent composites containing the absorbent compositions,
suitably in a concentration of up to about 100%, or about 65% or
more, or about 85% or more by weight of the absorbent cores or
composites. The absorbent composites may include between about 5%
and about 35% by weight natural, modified natural, and/or synthetic
fibers.
[0065] The fibers may include, but are not limited to, chemical
pulps such as sulfite and sulfate (sometimes called Kraft) pulps,
as well as mechanical pulps such as ground wood, thermomechanical
pulp and chemithermomechanical pulp. For example, the pulp fibers
may include cotton, typical wood pulps, cellulose acetate, rayon,
thermomechanical wood pulp, chemical wood pulp, debonded chemical
wood pulp, milkweed floss, and combinations thereof Pulps derived
from both deciduous and coniferous trees can be used. The fibers
may also be elastomeric or thermal binder fibers. Additionally, the
fibers may include such hydrophilic materials as microcrystalline
cellulose, microfibrillated cellulose, or any of these materials in
combination with wood pulp fibers.
[0066] A surfactant may also be added to the absorbent composite to
increase its wettability, or hydrophilicity. Examples of suitable
surfactants are commercially available from Uniqema in Wilmington,
Del., under the trade designation AHCOVEL, and from Cognis
Corporation in Cincinnati, Ohio, under the trade designation
GLUCOPON 220.
[0067] The absorbent composite can be formed on a coform line.
Coform processes combine separate polymer and additive streams into
a single deposition stream in forming a nonwoven web. One example
of such a process is disclosed in U.S. Pat. No. 4,100,324 to
Anderson et al., which is hereby incorporated by reference in its
entirety in a manner consistent with the present document. Another
example of a suitable process for forming an absorbent composite is
described in U.S. Pat. No. 5,350,624 to Georger et al., which is
also hereby incorporated by reference in its entirety in a manner
consistent with the present document. The polymers suitable for
forming coform nonwoven webs include any thermoplastic materials.
Examples include, but are not limited to, polyethylene,
polypropylene, polyester, polyamide, polyurethane, and elastomeric
thermoplastic materials, such as polyethylene elastomers,
polypropylene elastomers, polyester elastomers, polyisoprene,
cross-linked polybutadiene, diblock, triblock, or other multi-block
thermoplastic elastomeric and/or flexible copolymers.
[0068] The invention may also include absorbent articles containing
the absorbent composition. Examples of such suitable articles
include personal care absorbent articles, such as diapers, diaper
pants, baby wipes, training pants, absorbent underpants, child care
pants, swimwear, sanitary napkins, wipes, menstrual pads, changing
pads, menstrual pants, panty liners, panty shields, interlabials,
tampons, tampon applicators, incontinence products, urinary
shields, clothing components, bibs, shoe inserts, athletic and
recreation products; health/medical absorbent articles such as
products for applying hot or cold therapy, medical gowns (i.e.,
protective and/or surgical gowns), surgical drapes, caps, gloves,
face masks, bandages, wound dressings, wipes, covers, containers,
filters, disposable garments and bed pads, medical absorbent
garments, underpads; household/industrial absorbent articles such
as construction and packaging supplies, products for cleaning and
disinfecting, wipes, covers, filters, towels, disposable cutting
sheets, bath tissue, facial tissue, nonwoven roll goods,
home-comfort products including pillows, pads, cushions, masks and
body care products such as products used to cleanse or treat the
skin, laboratory coats, cover-alls, trash bags, stain removers,
topical compositions, laundry soil/ink absorbers, detergent
agglomerators, lipophilic fluid separators; and the like. Absorbent
composites consistent with the invention may be used in either a
single layer structure or a multi-layer structure, such as in a
dual layer structure wherein the absorbent composite may serve as
the upper layer, the lower layer, or both layers.
[0069] An example of a suitable absorbent article 120 into which
the absorbent composition may be incorporated is illustrated in
FIG. 10, and described in detail in U.S. Pat. No. 6,689,115 issued
Feb. 10, 2004, and incorporated herein by reference in its entirety
in a manner consistent with the present document. For example, the
absorbent composition may form all or part of an absorbent core
positioned between an outer cover and a body side liner of an
absorbent article. Because of the absorbent composition's
stickiness, the absorbent composition may be used in an unwrapped
state. More particularly, a tissue or other wrapping material may
not be required to contain the absorbent composition.
Test Methods
[0070] Centrifuge Retention Capacity (CRC) Test
[0071] The Centrifuge Retention Capacity (CRC) Test measures the
ability of the superabsorbent material to retain liquid therein
after being saturated and subjected to centrifugation under
controlled conditions. The resultant retention capacity is stated
as grams of liquid retained per gram weight of the sample (g/g).
The sample to be tested is prepared from particles which are
prescreened through a U.S. standard 30 mesh screen and retained on
a U.S. standard 50 mesh screen. As a result, the sample comprises
particles sized in the range of about 300 to about 600 microns. The
particles can be prescreened by hand or automatically and are
stored in a sealed airtight container until testing.
[0072] The retention capacity is measured by placing 0.2.+-.0.005
grams of the prescreened sample into a water-permeable bag which
will contain the sample while allowing a test solution (0.9 weight
percent sodium chloride in distilled water) to be freely absorbed
by the sample. A heat-sealable tea bag material, such as that
available from Dexter Corporation of Windsor Locks, Conn., U.S.A.,
as model designation 1234T heatsealable filter paper works well for
most applications. The bag is formed by folding a 5-inch by 3-inch
sample of the bag material in half and heat-sealing two of the open
edges to form a 2.5-inch by 3-inch rectangular pouch. The heat
seals should be about 0.25 inches inside the edge of the material.
After the sample is placed in the pouch, the remaining open edge of
the pouch is also heat-sealed. Empty bags are also made to serve as
controls. Three samples (e.g., filled and sealed bags) are prepared
for the test. The filled bags must be tested within three minutes
of preparation unless immediately placed in a sealed container, in
which case the filled bags must be tested within thirty minutes of
preparation.
[0073] The bags are placed between two TEFLON.RTM. coated
fiberglass screens having 3 inch openings (Taconic Plastics, Inc.,
Petersburg, N.Y.) and submerged in a pan of the test solution at 23
degrees Celsius, making sure that the screens are held down until
the bags are completely wetted. After wetting, the samples remain
in the solution for about 30.+-.1 minutes, at which time they are
removed from the solution and temporarily laid on a non-absorbent
flat surface. For multiple tests, the pan should be emptied and
refilled with fresh test solution after 24 bags have been saturated
in the pan.
[0074] The wet bags are then placed into the basket of a suitable
centrifuge capable of subjecting the samples to a g-force of about
350. One suitable centrifuge is a Heraeus LaboFuge 400 having a
water collection basket, a digital rpm gauge, and a machined
drainage basket adapted to hold and drain the bag samples. Where
multiple samples are centrifuged, the samples must be placed in
opposing positions within the centrifuge to balance the basket when
spinning. The bags (including the wet, empty bags) are centrifuged
at about 1,600 rpm (e.g., to achieve a target g-force of about
350), for 3 minutes. The bags are removed and weighed, with the
empty bags (controls) being weighed first, followed by the bags
containing the samples. The amount of solution retained by the
sample, taking into account the solution retained by the bag
itself, is the centrifuge retention capacity (CRC) of the sample,
expressed as grams of fluid per gram of sample. More particularly,
the retention capacity is determined as: 1 Sample & bag weight
after centrifuge - empty bag weight after centrifuge - dry sample
weight dry sample weight
[0075] The three samples are tested and the results are averaged to
determine the retention capacity (CRC) of the superabsorbent
material. The samples are tested at 23.+-.1 degrees Celsius at
50.+-.2 percent relative humidity.
[0076] 0.3 psi Pressure Swell Gel Bed Permeability (GBP)
[0077] As used herein, the Gel Bed Permeability (GBP) Under Load
Test, otherwise referred to herein as 0.3 psi pressure swell GBP,
determines the permeability of a swollen bed of gel particles under
conditions that are commonly referred to as being "under load"
conditions. The term "under load" means that swelling of the
particles is restrained by a load generally consistent with normal
usage loads applied to the particles, such as sitting, walking,
twisting, etc. by the wearer.
[0078] A suitable apparatus for conducting the Gel Bed Permeability
Test is shown in FIGS. 11 and 12 and indicated generally at 228.
The test apparatus 228 comprises a sample container, generally
indicated at 230, and a piston, generally indicated at 236. The
piston 236 comprises a cylindrical LEXAN shaft 238 having a
concentric cylindrical hole 240 bored down the longitudinal axis of
the shaft. Both ends of the shaft 238 are machined to provide upper
and lower ends respectively designated 242, 246. A weight,
indicated as 248, rests on one end 242 and has a cylindrical hole
bored through at least a portion of its center.
[0079] A circular piston head 250 is positioned on the other end
246 and is provided with a concentric inner ring of seven holes
260, each having a diameter of about 0.95 cm, and a concentric
outer ring of fourteen holes 254, also each having a diameter of
about 0.95 cm. The holes 254, 260 are bored from the top to the
bottom of the piston head 250. The piston head 250 also has a
cylindrical hole 262 bored in the center thereof to receive end 246
of the shaft 238. The bottom of the piston head 250 may also be
covered with a biaxially stretched 100 mesh stainless steel screen
264.
[0080] The sample container 230 comprises a cylinder 234 and a 400
mesh stainless steel cloth screen 266 that is biaxially stretched
to tautness and attached to the lower end of the cylinder. A gel
particle sample, indicated as 268 in FIG. 11, is supported on the
screen 266 within the cylinder 234 during testing.
[0081] The cylinder 234 may be bored from a transparent LEXAN rod
or equivalent material, or it may be cut from a LEXAN tubing or
equivalent material, and has an inner diameter of about 6 cm (e.g.,
a cross-sectional area of about 28.27 cm.sup.2), a wall thickness
of about 0.5 cm and a height of approximately 10 cm. Drainage holes
(not shown) are formed in the sidewall of the cylinder 234 at a
height of approximately 7.8 cm above the screen 266 to allow liquid
to drain from the cylinder to thereby maintain a fluid level in the
sample container at approximately 7.8 cm above the screen 266. The
piston head 250 is machined from a LEXAN rod or equivalent material
and has a height of approximately 16 mm and a diameter sized such
that it fits within the cylinder 234 with minimum wall clearance
but still slides freely. The shaft 238 is machined from a LEXAN rod
or equivalent material and has an outer diameter of about 2.22 cm
and an inner diameter of about 0.64 cm.
[0082] The shaft upper end 242 is approximately 2.54 cm long and
approximately 1.58 cm in diameter, forming an annular shoulder 247
to support the weight 248. The annular weight 248 has an inner
diameter of about 1.59 cm so that it slips onto the upper end 242
of the shaft 238 and rests on the annular shoulder 247 formed
thereon. The annular weight 248 can be made from stainless steel or
from other suitable materials resistant to corrosion in the
presence of the test solution, which is 0.9 weight percent sodium
chloride solution in distilled water. The combined weight of the
piston 236 and annular weight 248 equals approximately 596 grams
(g), which corresponds to a pressure applied to the sample 268 of
about 0.3 pounds per square inch (psi), or about 20.7
dynes/cm.sup.2 (2.07 kPa), over a sample area of about 28.27
cm.sup.2.
[0083] When the test solution flows through the test apparatus
during testing as described below, the sample container 230
generally rests on a 16 mesh rigid stainless steel support screen
(not shown). Alternatively, the sample container 230 may rest on a
support ring (not shown) diametrically sized substantially the same
as the cylinder 234 so that the support ring does not restrict flow
from the bottom of the container.
[0084] To conduct the 0.3 psi pressure swell Gel Bed Permeability
Test, the piston 236, with the weight 248 seated thereon, is placed
in an empty sample container 230 and the height is measured using a
suitable gauge accurate to 0.01 mm with the platen removed. It is
important to measure the height of each sample container 230 empty
and to keep track of which piston 236 and weight 248 is used when
using multiple test apparatus. The same piston 236 and weight 248
should be used for measurement when the sample 268 is later swollen
following saturation.
[0085] The sample to be tested is prepared from particles which are
prescreened through a U.S. standard 30 mesh screen and retained on
a U.S. standard 50 mesh screen. As a result, the test sample
comprises particles sized in the range of about 300 to about 600
microns. The particles can be prescreened by hand or automatically.
Also test samples can be as-is particles. Approximately 2.0 grams
of the sample are placed in the sample container 230 and spread out
evenly on the bottom of the sample container 230. The sample
container 230, with 2.0 grams of sample in it, and with the piston
236 and weight 248 placed on the sample within the sample container
230, is then submerged in the test solution for a time period of
about 60 minutes to saturate the sample.
[0086] At the end of this period, the sample container 230, piston
236, weight 248, and sample 268 are removed from the solution. The
thickness of the saturated sample 268 is determined by again
measuring the height from the bottom of the weight 248 to the top
of the cylinder 234, using the same thickness gauge used previously
provided that the zero point is unchanged from the initial height
measurement. The height measurement obtained from measuring the
empty sample container 230, piston 236, and weight 248 is
subtracted from the height measurement obtained after saturating
the sample 268. The resulting value is the thickness, or height "H"
of the swollen sample.
[0087] The permeability measurement is initiated by delivering a
flow of the test solution into the sample container 230 with the
saturated sample 268, piston 236, and weight 248 inside. The flow
rate of test solution into the sample container 230 is adjusted to
maintain a fluid height of about 7.8 cm above the bottom of the
sample container 230. The quantity of solution passing through the
sample 268 versus time is measured gravimetrically. Data points are
collected every second for at least twenty seconds once the fluid
level has been stabilized to and maintained at about 7.8 cm in
height. The flow rate Q through the swollen sample 268 is
determined in units of grams/second (g/s) by a linear least-square
fit of fluid passing through the sample 268 (in grams) versus time
(in seconds).
[0088] Permeability in cm.sup.2 is obtained by the following
equation:
K=[Q*H*.mu.]/[A*.rho.*P]
[0089] where K=Permeability (cm.sup.2), Q=flow rate (g/sec),
H=height of sample (cm), .mu.=liquid viscosity (poise)
(approximately one centipoises for the test solution used with this
Test), A=cross-sectional area for liquid flow (cm.sup.2),
.rho.=liquid density (g/cm.sup.3) (approximately one g/cm.sup.3,
for the test solution used with this Test) and P=hydrostatic
pressure (dynes/cm.sup.2) (normally approximately 3,923
dynes/cm.sup.2). The hydrostatic pressure is calculated from
P=.rho.*g*h
[0090] where .rho.=liquid density (g/cm.sup.3), g=gravitational
acceleration, nominally 981 cm/sec.sup.2, and h=fluid height, e.g.,
7.8 cm for the Gel Bed Permeability Test described herein.
[0091] A minimum of three samples is tested and the results are
averaged to determine the gel bed permeability of the sample.
[0092] Free Swell Gel Bed Permeability (GBP)
[0093] As used herein, the Gel Bed Permeability (GBP) Under Free
Swell Test, otherwise referred to herein as free swell GBP,
determines the permeability of a swollen bed of gel particles under
conditions that are commonly referred to as being "free swell" or
"no load" conditions. The term "free swell" means that swelling of
the particles is free without being restrained by an external
load.
[0094] The free swell GBP test is substantially the same as the 0.3
psi pressure swell GBP test set forth above, with the following
exception. After approximately 2.0 grams of the sample are placed
in the sample container 230 and spread out evenly on the bottom of
the sample container, the container, with 2.0 grams of sample in
it, without the piston 236 and weight 248 therein, is then
submerged in the test solution for a time period of about 60
minutes to saturate the sample and allow the sample to swell free
of any restraining load. At the end of this period, the piston 236
and weight 248 assembly is placed on the saturated sample 268 in
the sample container 230 and then the sample container 230, piston
236, weight 248, and sample 268 are removed from the solution. The
thickness of the saturated sample 268 is determined by again
measuring the height from the bottom of the weight 248 to the top
of the cylinder 234, using the same thickness gauge used
previously, provided that the zero point is unchanged from the
initial height measurement. The rest of the test procedure is the
same as that of the 0.3 psi pressure swell GBP test.
[0095] Wet Stickiness Test Method
[0096] To determine if a superabsorbent material is "wet sticky,"
the superabsorbent material is first sieved and 2 grams of 300 to
600 micron superabsorbent particles are poured into a 100 ml
PYREX.RTM. glass beaker and then 5 grams of 0.9 wt % NaCl saline
are added. If the particles stick together after the particles
swell (determined by picking up the gel bed with one's fingers and
more than 70%, suitably about 100%, of the swollen gels sticking
together), then the superabsorbent material is considered to
possess "wet stickiness."
[0097] Thermal Stickiness Test Method
[0098] To determine if a superabsorbent material is "thermally
sticky," the superabsorbent material is first sieved and 5 grams of
300 to 600 micron superabsorbent particles are poured into a 100 ml
PYREX.RTM. glass beaker. The glass beaker is then heated at a
temperature above the melting or softening temperature of the
thermoplastic surface treatment agent, for example, 150 degrees
Celsius for hydroxypropyl cellulose, for 10 minutes and then
completely cooled to room temperature (about 22 degrees Celsius).
Once the beaker is cooled, the beaker is then turned upside-down.
If less than about 30%, or less than about 1.5%, or 0%, by weight
of the particles fall out of the beaker upon being turned
upside-down, then the superabsorbent material is considered to
possess "thermal stickiness."
EXAMPLE
[0099] In this example, eight samples of superabsorbent material
were treated with various combinations of surface treatment agents.
The samples were tested for absorbency and stickiness properties.
The results are presented in Table 1.
[0100] Sample 0 was an untreated form of the same superabsorbent
material used in Samples 1-8, namely SXM 9543, available from
Degussa Superabsorber, Greensboro, N.C.
[0101] Sample 1 was prepared by combining 2.17 grams of polyvinyl
amine aqueous solution, available from BASF under the trade name
CATIOFAST.RTM. PR8106 at a solids level of 23 wt %, in a 250 ml
glass beaker with 48.33 grams of distilled water. The mixture was
stirred until a uniform solution was formed. While the solution was
being vigorously stirred, 20 grams of the dry superabsorbent powder
of Sample 0 were added to the solution. The superabsorbent powder
absorbed all the solution, and the partially swollen superabsorbent
particles were dried in an oven at 60 degrees Celsius for about 15
hours. The dried superabsorbent particles were pressed and sieved
through 30 (600 microns) and 50 (300 microns) mesh sieves. The
properties of the sieved particles between 300 and 600 microns are
presented in Table 1. FIG. 3 is representative of Sample 1.
[0102] Sample 2 was prepared by combining 1 gram of polyethylene
oxide powder, available from Union Carbide under the trade name
POLYOX.RTM. 205, in a 250 ml glass beaker with 50 grams of
distilled water. The mixture was stirred until a uniform solution
was formed. While the solution was being vigorously stirred, 20
grams of the dry superabsorbent powder of Sample 0 were added to
the solution. The superabsorbent powder absorbed all the solution,
and the partially swollen superabsorbent particles were dried in an
oven at 60 degrees Celsius for about 15 hours. The dried
superabsorbent particles were pressed and sieved through 30 (600
microns) and 50 (300 microns) mesh sieves. The properties of the
sieved particles between 300 and 600 microns are presented in Table
1. FIG. 4 is representative of Sample 2.
[0103] Sample 3 was prepared by combining 1 gram of polyethylene
oxide powder, available from Union Carbide under the trade name
POLYOX.RTM. 205, in a 250 ml glass beaker with 50 grams of
distilled water. The mixture was stirred until a uniform solution
was formed. While the solution was being vigorously stirred, 20.5
grams of polyvinyl amine surface-treated SXM 9543 prepared in the
same way as described in Sample 1 were added into the POLYOX.RTM.
solution. The superabsorbent material absorbed all the solution,
and the swollen superabsorbent particles were dried in an oven at
60 degrees Celsius for about 15 hours. The dried superabsorbent
particles were pressed and sieved through 30 (600 microns) and 50
(300 microns) mesh sieves. The properties of the sieved particles
between 300 and 600 microns are presented in Table 1. FIG. 5 is
representative of Sample 3.
[0104] Sample 4 was prepared by combining 2.17 grams of polyvinyl
amine aqueous solution, CATIOFAST.RTM. PR8106, in a 250 ml glass
beaker with 48.33 grams of distilled water. The mixture was stirred
until a uniform solution was formed. While the solution was being
vigorously stirred, 21 grams of polyethylene oxide surface-treated
SXM 9543 prepared in the same way as described in Sample 2 were
added into the CATIOFAST.RTM. PR8106 solution. The superabsorbent
material absorbed all the solution, and the swollen superabsorbent
particles were dried in an oven at 60 degrees Celsius for about 15
hours. The dried superabsorbent particles were pressed and sieved
through 30 (600 microns) and 50 (300 microns) mesh sieves. The
properties of the sieved particles between 300 and 600 microns are
presented in Table 1. FIG. 6 is representative of Sample 4.
[0105] Sample 5 was prepared by combining 0.5 gram of polyethylene
oxide powder (POLYOX.RTM. 205), 4.35 grams of polyvinyl amine
solution (CATIOFAST.RTM. PR8106), and 50 grams of distilled water
in a 250 ml glass beaker. The mixture was stirred until a uniform
solution was formed. While the solution was being vigorously
stirred, 20 grams of dry SXM 9543 superabsorbent powder were added
into the solution. The superabsorbent material absorbed all the
solution, and the partially swollen superabsorbent particles were
dried in an oven at 60 degrees Celsius for about 15 hours. The
dried superabsorbent particles were pressed and sieved through 30
(600 microns) and 50 (300 microns) mesh sieves. The properties of
the sieved particles between 300 and 600 microns are presented in
Table 1. FIG. 7 is representative of Sample 5.
[0106] Sample 6 was prepared by combining 2 grams of polyethylene
oxide powder (POLYOX.RTM. 205), 1.1 grams of polyvinyl amine
solution (CATIOFAST.RTM. PR8106), and 50 grams of distilled water
in a 250 ml glass beaker. The mixture was stirred until a uniform
solution was formed. While the solution was being vigorously
stirred, 20 grams of dry SXM 9543 superabsorbent powder were added
into the solution. The superabsorbent material absorbed all the
solution, and the partially swollen superabsorbent particles were
dried in an oven at 60 degrees Celsius for about 15 hours. The
dried superabsorbent particles were pressed and sieved through 30
(600 microns) and 50 (300 microns) mesh sieves. The properties of
the sieved particles between 300 and 600 microns are presented in
Table 1. FIG. 8 is representative of Sample 6.
[0107] Sample 7 was prepared by obtaining 20.5 grams of dry
polyvinyl amine surface-treated SXM 9543 prepared in the same way
as described in Sample 1, and spraying the surface-treated
superabsorbent material with water mist to a level of about 0.5
grams of water per gram of superabsorbent material. For example, 5
grams of water were sprayed onto 10 grams of dry superabsorbent
particles. After addition of the water moisture the superabsorbent
particles remained separatable and flowable. Next, 1 gram of dry
polyethylene oxide powder (POLYOX.RTM. 205) was added to the
partially wetted superabsorbent particles, and the combination was
stirred to achieve a uniform and even distribution. The treated
particles were dried in an oven at 60 degrees Celsius for 5 hours.
The dried superabsorbent particles were pressed and sieved again
through 30 (600 microns) and 50 (300 microns) mesh sieves. The
properties of the sieved particles between 300 and 600 microns are
presented in Table 1. FIG. 9 is representative of Sample 7.
[0108] Sample 8 was prepared by obtaining 20.5 grams of dry
polyvinyl amine surface-treated SXM 9543 prepared in the same way
as described in Sample 1, wetting the surface-treated
superabsorbent material with about 2 grams of an isopropyl
alcohol/water mixture (at a ratio of 3 to 1), and stirring the
combination to achieve a uniform distribution. Next, 1 gram of dry
polyethylene oxide powder (POLYOX.RTM. 205) was added to the wetted
superabsorbent particles, and the combination was vigorously
stirred to achieve a uniform and even distribution. The treated
particles were dried in an oven at 60 degrees Celsius for about 5
hours. The dried superabsorbent particles were pressed and sieved
again through 30 (600 microns) and 50 (300 microns) mesh sieves.
The properties of the sieved particles between 300 and 600 microns
are presented in Table 1. FIG. 9 is representative of Sample 8.
1TABLE 1 Properties of Treated Superabsorbent Materials Absorbency
Free 0.3 psi Surface Treatment Swell Swell CATIOFAST POLYOX .RTM.
CRC GBP GBP Stickiness Sample (wt %) (wt %) (g/g) (.times.10.sup.-8
cm.sup.2) (.times.10.sup.-8 cm.sup.2) Wet Thermal 0 0 0 23 31.2
14.5 No No 1 2.5 0 21 341.8 39.6 Yes No 2 0 5 23 24.0 No Yes 3 2.5
5 22 51.3 12.5 No Yes 4 2.5 5 21 103.7 27.7 Yes No 5 5 2.5 22 135.5
Yes No 6 1.25 10 22 44.8 No Yes 7* 2.5 5 21 145.3 28.6 Yes Yes 8*
2.5 5 21 138.2 Yes Yes Note: *An example of this invention
[0109] It will be appreciated that details of the foregoing
examples, given for purposes of illustration, are not to be
construed as limiting the scope of this invention. Although only a
few exemplary embodiments of this invention have been described in
detail above, those skilled in the art will readily appreciate that
many modifications are possible in the exemplary embodiments
without materially departing from the novel teachings and
advantages of this invention. Accordingly, all such modifications
are intended to be included within the scope of this invention,
which is defined in the following claims and all equivalents
thereto. Further, it is recognized that many embodiments may be
conceived that do not achieve all of the advantages of some
embodiments, particularly of the preferred embodiments, yet the
absence of a particular advantage shall not be construed to
necessarily mean that such an embodiment is outside the scope of
the present invention.
* * * * *